1. Field of the Invention
This invention relates generally to an alternating current generating device, and more specifically to an alternating current generating device of alternating current excitation type using an inductor-type high frequency generator for obtaining high output of low frequency, wherein circuits of simple configuration are provided to reduce the regulation of the voltage applied to the load.
2. Description of the Prior Art
The number of revolutions N of an ordinary AC generating device is generally expressed by the following equation. EQU N = 120 f/p (r.p.m.) (1)
where f is a frequency and p is the number of magnetic poles. In order to obtain a low frequency output of, for example, 50 Hz, the number of revolution N is limited to 3,000 rpm even when the number of magnetic poles p is set to 2 poles. For this reason, in designing a small-sized engine generator, there has been a limitation which make it impossible to increase the number of revolution to obtain high output.
To solve this problem, an AC generating device has been developed in which an inductor-type high frequency generator supplied with an AC field current of, for example, 50 Hz is revolved at high speed, and the resultant high frequency output is rectified and converted to a high output of a required frequency, for example, 50 Hz. In this type of AC generating device, however, the voltage regulation to a load is high, as often seen in conventional inductor-type high frequency generator, particularly a severe voltage regulation is observed when applied to a light load. To cope with this, there has been devised an automatic voltage regulating circuit provided at the output stage of the generating device. In this case, however, the current capacity of the automatic voltage regulating circuit tends to be too large. For this reason, there has been devised an AC generating device in which the field current is regulated in accordance with the voltage applied to the load. However, since an AC exciting type AC generator having a field current of sine wave is usually employed in such a device, the configuration of a control circuit for controlling the sine wave current at a predetermined level, or the above-mentioned automatic voltage regulating circuit becomes complicated. In addition, it is difficult to obtain a proper sine waveform.